Problem: $ { {3} \times \left[\begin{array}{rr}{4} & {1} \\ {-1} & {-1} \\ {4} & {0}\end{array}\right] = {?} } $
To multiply a matrix by a number, multiply each item of the matrix by the number. ${\left[\begin{array}{rr}{3}\times{4} & {3}\times{1} \\ {3}\times{-1} & {3}\times{-1} \\ {3}\times{4} & {3}\times{0}\end{array}\right]}$ Now, simplify: ${\left[\begin{array}{rr}{12} & {3} \\ {-3} & {-3} \\ {12} & {0}\end{array}\right]}$